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Filling Fingerboard Divots and Grooves on the Martin Ukulele

The neck is reset and the angle looks good.  This will probably be the best player out of all my Martin ukuleles when it's finished.

Now I'm going to fill the divots in the fingerboard and refret it.

In the first post of this series, I mentioned the green gunk that was on the fingerboard.  Here's what it looks like.  This is the 3rd fret just after I heated it with a soldering gun (100w, just a few seconds).  The green stuff literally boils up out of the fret slots!

It was all over the fingerboard, and I cleaned it off a year or so ago - read about it in my posts back then.  But it's everywhere!  And it was human-generated.  All the frets up to the 12th had this in their slots.  From the 12th fret onward, nothing.

Here all of the frets have been pulled.  I threw them away.  Useless now.  Notice the green tinge.

I just can't imagine playing an instrument with the fingerboard THAT dirty!  And it saw a lot of playing.

But when I'm done, the fingerboard will have a clean level surface, and we'll have nice new frets.

I just got this fret leveller tool from Stew-Mac.  This is the 8 inch version - perfect for an uku.  It's aluminum and pretty heavy.  You attach your sandpaper on one edge and you can level fingerboards or frets.

Here it is in action.  Stew-Mac sells sandpaper strips with an adhesive back you can attach to the tool.  I just cut my own sandpaper and attached it with a light coat of 3M adhesive spray.

The strips are probably more convenient, though.

I went over the board with 220 grit and then 320.  It's perfectly level and looks good.

What doesn't look good are the divots in the board.  Sanding it didn't have an effect, no surprise there.

I tried to get a shot that shows just how deep the worst divots are.  It's hard to show them, but if you look at the difference between the bottom of the gauge and the depth of the divots you get an idea.  I roughly measured them at about .050 of an inch!

Whoever played this ukulele played it a lot.  There's heavy wear on each position on the first four frets, and significant wear up to the 7th fret.  They also had long nails.  Maybe it was a woman?  Whoever it was was a player for sure.   These are the deepest divots I've ever seen.  And ironically, it's on an instrument with nylon strings.  The fretwear was heavy too.

This repair won't be perfect, but it will let me level the fingerboard.  This is the famous Frank Ford technique.

Make deep lengthwise cuts in the board with an X-acto.

Then use the knife to pull the slivers of wood you've cut upward.  The idea is to make a 'nest' of wood fibers.

Here's what I wound up with.  I used 2 blades during this process.  A new blade will give you a deeper and thinner cut.

Then we take some rosewood dust and sprinkle it onto the fingerboard.  Sort of like magic dust, except it's rosewood.

I had a rosewood bridge blank on hand and I filed some dust and also sanded some onto a sheet of paper to try and get a mix of textures - the bigger fibers, the more medium file shavings, and then the sawdust.

After sprinkling it on, pack it down into the divots.

Then I put drops of medium CA onto each pile covering the divots.  Last time I did this, I used thin CA.  That might be better - the medium takes a while to soak into the sawdust pile.

Also see what happens when you have a dropper of CA in one hand and a camera in the other!  Get that superglue off quickly!  You can get the excess of the fingerboard if needed with acetone, but you can't use acetone on a lacquer finish!

Freshly filled.  I let this dry overnight - there is so much CA that it takes a while.

After it's dry, I'll scrape off most of the excess and sand the board again.  I'm expecting to have to do a second fill, but we'll see how this one worked soon enough.


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